/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * Helper function for testing code in interrupt contexts
 *
 * Copyright 2025 Google LLC
 */
#ifndef _KUNIT_RUN_IN_IRQ_CONTEXT_H
#define _KUNIT_RUN_IN_IRQ_CONTEXT_H

#include <kunit/test.h>
#include <linux/timekeeping.h>
#include <linux/hrtimer.h>
#include <linux/workqueue.h>

struct kunit_irq_test_state {
        bool (*func)(void *test_specific_state);
        void *test_specific_state;
        bool task_func_reported_failure;
        bool hardirq_func_reported_failure;
        bool softirq_func_reported_failure;
        atomic_t task_func_calls;
        atomic_t hardirq_func_calls;
        atomic_t softirq_func_calls;
        ktime_t interval;
        struct hrtimer timer;
        struct work_struct bh_work;
};

static enum hrtimer_restart kunit_irq_test_timer_func(struct hrtimer *timer)
{
        struct kunit_irq_test_state *state =
                container_of(timer, typeof(*state), timer);
        int task_calls, hardirq_calls, softirq_calls;

        WARN_ON_ONCE(!in_hardirq());
        task_calls = atomic_read(&state->task_func_calls);
        hardirq_calls = atomic_inc_return(&state->hardirq_func_calls);
        softirq_calls = atomic_read(&state->softirq_func_calls);

        /*
         * If the timer is firing too often for the softirq or task to ever have
         * a chance to run, increase the timer interval.  This is needed on very
         * slow systems.
         */
        if (hardirq_calls >= 20 && (softirq_calls == 0 || task_calls == 0))
                state->interval = ktime_add_ns(state->interval, 250);

        if (!state->func(state->test_specific_state))
                state->hardirq_func_reported_failure = true;

        hrtimer_forward_now(&state->timer, state->interval);
        queue_work(system_bh_wq, &state->bh_work);
        return HRTIMER_RESTART;
}

static void kunit_irq_test_bh_work_func(struct work_struct *work)
{
        struct kunit_irq_test_state *state =
                container_of(work, typeof(*state), bh_work);

        WARN_ON_ONCE(!in_serving_softirq());
        atomic_inc(&state->softirq_func_calls);

        if (!state->func(state->test_specific_state))
                state->softirq_func_reported_failure = true;
}

/*
 * Helper function which repeatedly runs the given @func in task, softirq, and
 * hardirq context concurrently, and reports a failure to KUnit if any
 * invocation of @func in any context returns false.  @func is passed
 * @test_specific_state as its argument.  At most 3 invocations of @func will
 * run concurrently: one in each of task, softirq, and hardirq context.  @func
 * will continue running until either @max_iterations calls have been made (so
 * long as at least one each runs in task, softirq, and hardirq contexts), or
 * one second has passed.
 *
 * The main purpose of this interrupt context testing is to validate fallback
 * code paths that run in contexts where the normal code path cannot be used,
 * typically due to the FPU or vector registers already being in-use in kernel
 * mode.  These code paths aren't covered when the test code is executed only by
 * the KUnit test runner thread in task context.  The reason for the concurrency
 * is because merely using hardirq context is not sufficient to reach a fallback
 * code path on some architectures; the hardirq actually has to occur while the
 * FPU or vector unit was already in-use in kernel mode.
 *
 * Another purpose of this testing is to detect issues with the architecture's
 * irq_fpu_usable() and kernel_fpu_begin/end() or equivalent functions,
 * especially in softirq context when the softirq may have interrupted a task
 * already using kernel-mode FPU or vector (if the arch didn't prevent that).
 * Crypto functions are often executed in softirqs, so this is important.
 */
static inline void kunit_run_irq_test(struct kunit *test, bool (*func)(void *),
                                      int max_iterations,
                                      void *test_specific_state)
{
        struct kunit_irq_test_state state = {
                .func = func,
                .test_specific_state = test_specific_state,
                /*
                 * Start with a 5us timer interval.  If the system can't keep
                 * up, kunit_irq_test_timer_func() will increase it.
                 */
                .interval = us_to_ktime(5),
        };
        unsigned long end_jiffies;
        int task_calls, hardirq_calls, softirq_calls;

        /*
         * Set up a hrtimer (the way we access hardirq context) and a work
         * struct for the BH workqueue (the way we access softirq context).
         */
        hrtimer_setup_on_stack(&state.timer, kunit_irq_test_timer_func,
                               CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
        INIT_WORK_ONSTACK(&state.bh_work, kunit_irq_test_bh_work_func);

        /*
         * Run for up to max_iterations (including at least one task, softirq,
         * and hardirq), or 1 second, whichever comes first.
         */
        end_jiffies = jiffies + HZ;
        hrtimer_start(&state.timer, state.interval, HRTIMER_MODE_REL_HARD);
        do {
                if (!func(test_specific_state))
                        state.task_func_reported_failure = true;

                task_calls = atomic_inc_return(&state.task_func_calls);
                hardirq_calls = atomic_read(&state.hardirq_func_calls);
                softirq_calls = atomic_read(&state.softirq_func_calls);
        } while ((task_calls + hardirq_calls + softirq_calls < max_iterations ||
                  (task_calls == 0 || hardirq_calls == 0 ||
                   softirq_calls == 0)) &&
                 !time_after(jiffies, end_jiffies));

        /* Cancel the timer and work. */
        hrtimer_cancel(&state.timer);
        flush_work(&state.bh_work);

        /* Sanity check: the timer and BH functions should have been run. */
        KUNIT_EXPECT_GT_MSG(test, atomic_read(&state.hardirq_func_calls), 0,
                            "Timer function was not called");
        KUNIT_EXPECT_GT_MSG(test, atomic_read(&state.softirq_func_calls), 0,
                            "BH work function was not called");

        /* Check for failure reported from any context. */
        KUNIT_EXPECT_FALSE_MSG(test, state.task_func_reported_failure,
                               "Failure reported from task context");
        KUNIT_EXPECT_FALSE_MSG(test, state.hardirq_func_reported_failure,
                               "Failure reported from hardirq context");
        KUNIT_EXPECT_FALSE_MSG(test, state.softirq_func_reported_failure,
                               "Failure reported from softirq context");
}

#endif /* _KUNIT_RUN_IN_IRQ_CONTEXT_H */